Hydraulic track adjusters used on crawler tractors between the recoil spring and the idler commonly have a variable volume fluid chamber into which grease or oil is added to extend a rod or piston for tightening the track chain to compensate for wear to the track components. Many of such track adjusters include a fill valve for adding pressurized fluid to the chamber and a separate relief valve for venting the chamber in preparation for disassembling the track chain. During initial filling of the fluid chamber, the relief valve is normally open slightly to purge trapped air from the chamber as fluid is pumped into the chamber through the fill valve.
Another type of track adjuster uses a single fill valve which also functions as a vent valve for venting the chamber prior to disassembly of the recoil mechanism or for relieving the tension on the tracks for adjustment. One of the problems encountered with track adjusters having only a single fill valve is that of purging the air from the adjusting chamber during the initial filling of the chamber particularly when the recoil mechanism is in place on the tractor. Proper operation of the recoil mechanism is dependent upon the adjusting chamber not having any air trapped therein. If air is trapped within the adjusting cylinder, the track adjuster is spongy and proper track adjustment cannot be maintained.